This invention relates generally to the improvement in an internal combustion engine of the type wherein the number of engine cylinders operated is controlled to be changed in accordance with engine operating conditions, and more particularly to a device for improving engine brake of the same engine.
In order to improve fuel economy during urban area cruising of a motor vehicle, it has already been proposed that the supply of fuel and air into some cylinders is stopped so that an engine is operated by the power generated in the remaining operated engine cylinders, during engine deceleration and light load engine operation. The number of the cylinders not operated is usually selected to be three in the case of a six-cylinder engine from a point of view of engine balancing. However, by thus stopping the fuel and air supply to the some cylinders, a high vacuum is generated in these cylinders to increase the so-called pumping loss and accordingly engine brake (brake by engine deceleration) becomes effective thereby. This provides resistance to the operation of the remaining operated cylinders which are supplied with fuel and air, unavoidably decreasing engine output power.
In this regard, it has also already been proposed that the engine cylinders not operated are supplied with fresh air or exhaust gas to decrease the pumping loss. However, even the thus arranged engine has encountered a problem in which the engine brake is not effective when brake is required to slow down the speed of the motor vehicle, because of the decreased pumping loss.